The invention relates to a hammer-tool.
Hammer-tools of the prior art work on the principle of acceleration of a striker piston by compressed air applied thereto and, depending on the construction of the valve at the inlet orifice of the cylinder and on the ducting of compressed air in the housing, they are designed either for producing continually repeated fast striker or hammer movements or for producing single individual hammer blows. For driving fastener bolts, those types of tools in which in each case only one single hammer blow is triggered on tool action, are of special interest. For this reason it is advisable to arrange for the piston to pick up a considerable amount of kinetic energy along its acceleration path, which however must not also apply to the return stroke or the piston because in that event the impact of the latter inside the cylinder would cause serious damage. For this reason the venting pipe which in conventional hammer tools serve at the same time for the supply of compressed air for the return stroke of the piston, after appropriate valve-actuation, is provided with a correspondingly small cross section so that only a restricted amount of compressed air, as compared with the operative hammer blow, can be applied to the rear side of the striker piston and consequently the latter only acquires a correspondingly reduced speed. This means that during the operative hammer blow the outflowing air must also surmount the throttle effect of the vent aperture and this limits acceleration. A further limitation resides in that the inlet to the cylinder can only be progressively opended on valve actuation at a comparatively slow speed. This means that the striker piston commences its operative stroke under an initially still very small charge and has already covered a portion of its operative travel by the time it receives the full compressed air charge. Thus only an abbreviated residual travel distance and correspondingly shortened time remains available for maximum possible acceleration.